U.S. Pat. App. Ser. No. 09/244,729, filed Feb. 5, 1999, is incorporated herein by reference. The present invention relates to methods and devices for extending the life of an x-ray tube. Typically x-ray tubes are mounted inside a lead shielded radiation enclosure called a housing or casing. The housing is attachable to the x-ray machine, typically a CT, fluoroscopic, or rad machine. The housing is filled with a fluid of synthetic or petroleum derivative, generally referred to as insulating oil. The insulating oil acts to thermally and electrically insulate the tube. Heat is generally removed to air through fluid to water or fluid to water cooled air transfer.
All such fluids, are damaged, from four major contributors: (1) heat; (2) radiation; (3) high voltage arcing; and (4) corona discharge.
This heating oil is sold by two primary standards: (1) ASTM 877 for unprocessed oil; and (2) ASTM 1816 for processed oil. Insulating oil consists of perhaps 3500 separate hydrocarbons. The hydrocarbons having varying carbon bond lengths with many separate bonded molecules and ions, such as hydrogen, oxygen, hydroxyls, and many others.
For most x-ray products, the end of life is primarily predicated by an arcing process. Failure is accentuated by deposition on the glass or metal window of the insert. Deposition on the high voltage hold off leads to collapse in the insert itself, leading to subsequent deterioration of rotor function. The arcing while starting out infrequently, increases in frequency as the oil deteriorates. As the arcing increases the oil deteriorates more rapidly which, in turn, leads to more arcing.
It is commonly thought that the greases and waxes produced during the life of an x-ray tube are deleterious to the insulating oil, i.e. damaging. Such is the motivation behind U.S. Pat. No. 5,440,608 entitled "Method And System For Extending The Service Life Of An X-Ray Tube" by Peralta, et al. The method taught in Pat. '608, and subsequent patents by Peralta, U.S. Pat. Nos. 5,596,622 and 5,732,123. U.S. Pat. Nos. 5,440,608; 5,732,123; and 5,596,622 are collectively referred to herein as PERALTA. PERALTA describes methods and apparatus for removing the old oil and replacing it with new oil, and methods for filtering the greases and waxes produced during the life of an x-ray tube. As PERALTA points out, the financial risks involved in when working with x-ray tubes and CT scanners is substantial. Tubes are very delicate in some respects and require great care when repairing them.
One problem encountered in the past has been the removal of bubbles which has come out of solution, or removal of those introduced into the system when oil has been replaced. For Siemens and Phillips manufactured tubes it has been quite common for many years to remove bubbles by replacing the oil. Circa 1984, General Electric introduced quick-disconnects into the hydraulic system, i.e. quick-disconnects in-line between the heat exchanger and the x-ray tube housing. This facilitated the removal of bubbles from the system. Since approximately 1985, this inventor has had occasion to open the hoses between the heat exchanger and the x-ray tube to remove bubbles, or replace oil, or both. PERALTA describes these well known techniques.
This inventor believes the greases and waxes are not as damaging as is commonly believed. In fact, the addition of new oil, as taught by Peralta, is contrary to preferred embodiments of the present invention.